When print images are generated on a carrier material with the aid of an electrophotographic printer or copier, positioning errors of a toner image generated on a toner image carrier with respect to a carrier material to be printed with the toner image occur particularly due to the structure and the sequence of the printing process in the printer or copier.
Register errors result from these positioning errors, especially when the carrier material is printed on several times and when multicolor documents are generated, and then the generated print images are not superimposed in a register-accurate manner. When the toner image carrier, for example, a transfer belt, is brought into contact with a carrier material to be printed, positional displacements of the print image in the range of ≦2 mm occur in known high-performance printers, which positional displacements cannot be reduced further by way of a mechanical adjustment at an acceptable expense.
Particularly in the case of multicolor printing, these print image displacements are, however, visible when several color separations successively applied to the carrier material are not positioned exactly on top of one another. And likewise, printing a print image on a carrier material and arranging a second print image exactly next to the first print image after an interruption of the printing process is difficult due to the possible positioning errors described since, in particular, the overlapping of the print images is disturbing and has to be avoided.
International patent application WO 00/54266 discloses a device for transferring at least one toner image from a toner image carrier belt onto a carrier material. In this process, the toner image carrier belt is guided such that in the case of a swivel motion of a roll device, the belt tension always remains the same. For transfer printing the toner image present on the toner image carrier belt onto the carrier material, the surface of the toner image carrier belt with the toner image present thereon is brought into contact with the surface of the carrier material via the swivel motion of the roll device, i.e., the carrier material is contacted by the toner image carrier belt.
International patent application WO 00/34831 discloses an electrophotographic printing device comprising a photoconductor and a transfer belt, a toner image to be transferred onto a carrier material being generated on the photoconductor and being transferred onto the transfer belt. Subsequently, the toner image transferred onto the transfer belt is transfer-printed onto a carrier material. In addition to the print image to be generated on the carrier material, a position mark is generated from toner material on the photoconductor, which mark is likewise transfer-printed onto the transfer belt and is detected via a sensor. The running time of the toner mark from its generation on the photoconductor up to the time of detection at the sensor is determined, and the transport of the carrier material is controlled dependent on the running time determined.
U.S. Pat. No. 4,475,805, International Patent publication no. WO 2000/34 831 A1, and German Patent document nos. DE 44 17 807 A1 and DE 195 42 612 A1 disclose further electrophotographic image generating devices.
The positional errors occurring during the contacting of the carrier material with the transfer belt at the start of the printing process for generating a new print image on the carrier material can, at present, not be prevented with the known methods for high-performance printers or copiers. The known devices serve to guarantee an exact positioning during a continuous printing process. A method or an arrangement for the effective prevention of positioning errors occurring during a start of the printing process, particularly due to the contacting of the transfer belt with the carrier material, is, at present, not known in the prior art. In particular, when a print image is joined flush with a print image that has already been printed on the carrier material in a preceding printing process and when several color separations are printed on top of one another, these positioning errors are visible in the generated print image.